Fabric wipes having color indicators are disclosed in U.S. Pat. No. 4,311,479, issued to Fenn et al., and in U.S. Pat. No. 4,678,704, issued to Fellows. Fenn et al. discloses a cloth impregnated with an antimicrobial composition that is activated upon contact with a liquid such as water, and is ionically bonded to the cloth. Small portions of the impregnated cloth are dyed with an indicator dye which bonds preferentially to the antimicrobial composition so that when the antimicrobial composition is exhausted, the dye will disappear from the cloth.
Fellows discloses an impregnated fabric material having an active cationic impregnant bonded to its fabric substrate. An anionic indicator dye in combination with a further cationic component is also bonded to the substrate. The dye bonds to the further cationic component more readily than to the substrate and the further cationic component competes with the impregnant for bonding to the dye. In the case of a wiping cloth, when the dye has been removed to indicate exhaustion of the active component, enough active component remains on the cloth to provide a safety margin.
These and similar prior art fabrics had color indicators to indicate the dissipation of impregnant. Yet the indicators only worked once, and only changed color once. If the fabric was then recharged with impregnant, such as by dipping it into a bucket, the original color would not return and the indicator function would not return.
Co-pending U.S. patent application Ser. No. 12/702,138 to Farrugia et al., filed on 8 Feb. 2010, addresses this problem to some degree by providing a reversible color-changing sanitizer indicator. The reversible color-changing ink formulation includes about 10-50% by weight of a polymer binder, about 10-50% by weight of a wetting agent, about 0-10% by weight of an ionic stabilizer, and about 1-10% by weight of an anionic indicator compound, based on a dry weight of the ink formulation. The color-changing ink formulation is bound to the nonwoven fabric wipe using the polymer binder. Suitable polymer binders include cellulose acetate and cellulose acetate derivatives.
While polymer binder concentrations near the high end of the range described in Farrugia may increase the binding properties of the ink formulation, they also diminish or dilute the color provided by the ink formulation. There is a need or desire for a reversible color-changing ink formulation and nonwoven wipes that can utilize a higher amount of other polymer binders and thus provide more durable binding, while providing sufficient color.